FUNCTION: [Summary is not available for the mouse gene. This summary is for the human ortholog.] Prader-Willi syndrome (PWS) is caused by the loss of expression of imprinted genes in chromosome 15q11-q13 region. Affected individuals exhibit neonatal hypotonia, developmental delay, and childhood-onset obesity. Necdin (NDN), a gene involved in the terminal differentiation of neurons, localizes to this region of the genome and has been implicated as one of the genes responsible for the etiology of PWS. This gene is structurally similar to NDN, is also localized to the PWS chromosomal region, and is paternally imprinted, suggesting a possible role for it in PWS. [provided by RefSeq, Oct 2010] PHENOTYPE: Mice heterozygous for a null allele that is inherited paternally exhibit some postnatal lethality, reduced male fertility, abnormal circadian rhythm, and hypoactivity. Mice heterozygous for another paternal knock-out allele exhibit 50% neonatal lethalityassociated with weak suckling activity. [provided by MGI curators]